Brain Analgesia System
Dr Ghulam Mustafa
Learning objectives
• What is brain analgesia system
• Enlist components of analgesia system
• Enlist chemical mediators of analgesia system
• Describe mechanism of working of analgesia
system
• Explain the physiological mechanism involved in
referred pain
nucleus reticularis
paragigantocellularis-
Brain Analgesia System
Endogenous capability of the brain itself
to suppress the input of pain signals to
the nervous system by activating a pain
control system, called an analgesia
system.
The analgesia system
1) The periaqueductal gray and periventricular
areas of the mesencephalon and upper pons
surround the aqueduct of Sylvius and portions
of the third and fourth ventricles.
from these areas signals to
2) The raphe magnus nucleus located in the lower pons and upper medulla
The nucleus reticularis paragigantocellularislocated laterally in the medulla.
second-order signals are transmitted to
(3) a pain inhibitory complex located in the
dorsal horns of the spinal cord.
• Analgesia signals can block the pain
before it is relayed to the brain.
Suppression of strong pain signals
• Electrical stimulation
– Peri aqueductal gray area
– Raphe Magnus nucleus
– Areas – higher levels of the brain that excite
the Peri aqueductal gray
• Periventricular nuclei in the hypothalamus
• Medial forebrain bundle, in the hypothalamus.
• Suppress strong pain signals entering by
way of the dorsal spinal roots.
Transmitter substances involved in
analgesia system
• Nerve fibers from periventricular nuclei and
periaqueductal gray area secrete
– Enkephalin
• Fibers originating in Raphe Magnus send
signals to dorsal horns of the spinal cord to
secrete
– Serotonin
• The serotonin causes local cord neurons to
secrete
– Enkephalin
Functions of Enkephalin
• Enkephalin cause
– Presynaptic and
– Postsynaptic
• Inhibition of incoming
– Type C and
– Type A Delta pain fibers….
• Where they synapse in the dorsal horns.
• The analgesia system can block pain signals
at the initial entry point to the spinal cord.
Brain’s Opiate System
• Injection of minute quantities of morphine
– Either into the periventricular nucleus around the
third ventricle or
– Into the periaqueductal gray area of the brain stem
• Causes an extreme degree of analgesia.
• Morphine-like agents – opiates:
– Act at many other points in the analgesia system,
including the dorsal horns of the spinal cord
• Opiate-like substances - found at different
points of the nervous system
– Breakdown products of three large protein
molecules:
• Proopiomelanocortin,
• Proenkephalin, and
• Prodynorphin.
• Important opiate-like substances are
– β-endorphin,
– Met-enkephalin,
– Leuenkephalin
– Dynorphin.
Activation of
THE ANALGESIA SYSTEM
by nervous signals entering
the periaqueductal gray and periventricular areas,
or
Inactivation of
Pain pathways by morphine-like drugs,
can almost totally
suppress many pain signals entering through
the
peripheral nerves.
Inhibition of Pain Transmission by Tactile
Sensory Signals
• Stimulation of large type Aβ sensory fibers
– from peripheral tactile receptors
– depress transmission of pain signals
• from the same body area.
• Local lateral inhibition in the spinal cord
• The simultaneous
– physical and
– psychogenic excitation of the central analgesia
system
• the basis of pain relief by ACUPUNCTURE.
Treatment of Pain by Electrical
Stimulation
• Stimulating electrodes are
– Placed on selected areas of the skin
– Implanted over the spinal cord
• To stimulate the dorsal sensory columns.
• Electrodes placed in
– Appropriate intralaminar nuclei of the
thalamus or
– in the periventricular or periaqueductal
area of the diencephalon.
Referred Pain
• Pain in a part of the body that is fairly remote
from the tissue causing the pain. This is called
referred pain.
• Important in clinical diagnosis
Mechanism of Referred Pain.
• Branches of visceral pain fibers synapse in the
spinal cord
– on the same second-order neurons (1 and 2)
– Receive pain signals from the skin.
• When the visceral pain fibers are stimulated……
Localization of Referred Pain from Viscera
• Localizes in dermatomal segment - visceral
organ originated in the embryo,
• Heart originated - neck and upper thorax,
• The heart’s visceral pain fibers
– Pass upward along the sympathetic sensory nerves
– Enter spinal cord between segments C-3 and T-5.
• Pain from the heart
–
–
–
–
–
Referred to the side of the neck,
Over the shoulder,
Over the pectoral muscles,
Down the arm,
Substernal area of the upper chest